The art of coating particulate material is an old and crowded one. Spherical granules (beadlets), otherwise regularly shaped granules or irregularly shaped granules (all referred to as particles) of therapeutic materials are coated with coating material that is less soluble, or soluble under different conditions of pH, for example, than the enrobed particles, to produce a delayed or timed release of the medicament. Particles of disagreeable-tasting substances are coated to mask the taste. Other coatings are provided to protect the coated particles from the atmosphere or moisture. Rice has been coated with carboxy methylcellulose containing vitamins lost in the polishing process. Inert or therapeutically inactive carrier particles have been coated with silicone oil, for example to serve as an eructant. The coating has been accomplished in a number of ways, by spraying, mixing, tumbling, and, particularly in the case of the therapeutic materials coated for delayed release, by suspending the particles in a matrix of coating material, and spinning the mixture from a disc in the form of droplets or shearing the attenuated mixture at the periphery of the disc to form droplets which are then solidified by cooling, driving off of solvent, polymerization, or some combination of these processes.
A method and apparatus for coating granular salt material has been proposed, in U.S. Pat. No. 2,955,956, in which a liquid slurry of additive material is introduced centrally to a rotating plate, granular salt material is introduced to the surface of the plate radially outboard of the liquid slurry and inboard of the edge of the plate, and the coated salt is discharged from the periphery. However, that arrangement has the disadvantage of discharging excess slurry as well. In the case of a therapeutic material, this would mean that there were particles of active material and particles of inactive material which would have somehow to be sorted if known dosages were to be obtained.
A method and apparatus involving the centrifugal slinging of metal chips up the side of a conical bowl and over the upper edge have been proposed, in U.S. Pat. No. 4,298,476 but the object of that method and apparatus, is to separate the chips from lubricant, not to coat them, the lubricant being discharged through a porous part of the bowl and the separated chips being carried out by entrainment in a current of air.
In both of these patents, the plate or bowl has been rotated from beneath. It can be seen, however, that a plate or bowl can be driven by a motor mounted above them. In the embodiment of apparatus of the present inventions shown and described, the details of the motor drive and various feed mechanisms are not shown in detail because they are well within the skill of the ordinary mechanic and may be varied to meet the demands of volume of material to be treated, types of particulate material and nature of the coating materials, for example.
One of the objects of this invention is to provide a method and apparatus for coating granular material in such a way that the coated granular material is unmixed with droplets of coating material.
Another object is to provide such a method and apparatus that can be used in connection with various different kinds of granular materials and different coatings.
Yet another object is to provide such a method and apparatus that is simple, easy to use, and effective to produce a substantially uniform and reproducible resultant product.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.